Expandable bit screw holding screwdriver

ABSTRACT

A screw holding screwdriver includes a two piece longitudinally split shank which terminates at its forward ends in a dovetailed expandable bit comprised of two driving tips wedge-shaped in cross section. The bit is expandable laterally by wedging together the tips using a forwardly movable sleeve encircling the shank. In a second embodiment, the expandable bit is longitudinally self-centering within a straight screw slot, the ends of which are engageable with the thick outer wedge portions of the driving tips projecting outwardly from either end and longitudinally thereof.

United States Patent Benitz Aug. 19, 1975 1 EXPANDABLE BIT SCREW HOLDING SCREWDRIVER [76] Inventor: Earl Benitz, P.O. Box 106,

Petersburg, Alaska 99833 [22] Filed: Apr. 23, I974 21 Appl. No.: 463,208

[52] US. Cl 145/50 E [51] Int. Cl. B25b 15/02 [58} Field of Search 145/50 E, 50 D, 50 A [56] References Cited UNITED STATES PATENTS 1,275,810 l/l9l8 White 145/50 E FOREIGN PATENTS OR APPLICATIONS 429,219 l/l948 Italy 145/50 E 300,375 7/1954 Switzerland. 828,228 7/1949 Germany 145/50 E 222,808 12/1957 Australia 145/50 E 166,083 8/1947 Austria 145/50 E Primary Examiner-Al Lawrence Smith Assistant Examiner-Marc R. Davidson Attorney, Agent, or Firm-Christensen, OConnor,

Garrison, & Havelka [5 7] ABSTRACT A screw holding screwdriver includes a two piece longitudinally split shank which terminates at its forward ends in a dovetailed expandable bit comprised of two driving tips wedge-shaped in cross section. The bit is expandable laterally by wedging together the tips using a forwardly movable sleeve encircling the shank. In a second embodiment, the expandable bit is longitudinally self-centering within a straight screw slot, the ends of which are engageable with the thick outer wedge portions of the driving tips projecting outwardly from either end and longitudinally thereof.

2 Claims, 6 Drawing Figures PATENTED 1 1 3.900.057

lull

EXPANDABLE BIT SCREW HOLDING SCREWDRIVER BACKGROUND OF THE INVENTION This invention relates to screw holding screwdrivers and, more particularly, to an improved expandable bit screw holding screwdriver generally of the type which is illustrated and described in U.S. Pat. No. 3,224,479 issued to C. M. Osborn et al. on Dec. 21, I965, and in US. Pat. No. 2,445,383 issued to G. W. Barlow on July 20, I948.

' In these prior devices the two parts or halves of the longitudinally split shank are wedged together by advancement toward the bit of the actuator sleeve which drives the tips apart. However, relief cuts in the wedging surfaces near the tips cause the tips to separate as the sleeve advances. The tips are flexed toward each other with increase in pressure against the opposite screw slot walls and hence the shank parts are sprung away from each other. Consequently security of engagement with the screw head depends on resilient stiffness of the shank parts and the tips, and with screws hard to drive the two tips forming the bit can yield and shift relatively. Thus it is found that for many applications these prior devices are unstable and slip from the screw.

It is an object of the present invention to provide an improved screw holding expandable bit screwdriver of the type generally described, having two complemental driving tips so devised as to remain in continual abutting unyielding engagement with one another and which will not shift or become dislodged from the screw. A related object is to provide such a screwdriver which can be utilized more effectively to both start and drive a screw.

Another object is to provide a screwdriver of the type described which tends to be self-centering longitudi nally of the straight screw slot.

A specific object hereof is to provide a screw holding screwdriver having an improved expandable bit form more secure in its engagement with standard straight screw slots and especially so when used with dovetail screw slots made for the purpose.

SUMMARY OF THE INVENTION In accordance with the principles of the present invention, an expandable bit screw holding screwdriver is provided. The screw holding screwdriver includes a handle from which projects an elongated shank. The shank is split longitudinally into two resilient overlappingly superimposed parts having substantially planar mutual inner contact faces extending longitudinally thereof and along which the shank parts diverge proceeding forwardly. The shank parts each terminate in driving tips of reduced thickness and of wedge-shaped cross section. The tips include longitudinal outer faces inclined to the contact faces, which respectively continue forwardly from the shank part contact faces. That is, the tips are in continual abutting unyielding engagement with each other along their contact faces. A longitudinally movable sleeve encircling the shank parts when slidably moved toward the forward end of the shank progressively decreases the divergence between the shank parts and thus correspondingly increases the thickness of the bit made up by the tips. In accordance with further principles of this invention, the longitudinal outer faces are tapered inwardly toward the rear of the shank. According to a second preferred embodiment of this invention, the outer thickness of each tip is greater than the combined central thicknesses of their relatively thin inner overlapping portions. That is, the bit made up by the tips has opposite outwardly opening generally V-shaped notches.

It will be appreciated from the foregoing summary that the invention provides a screw holding expandable bit screwdriver suitable for use with screws having standard and dovetail slots, The bit formed by the driving BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective of the screwdriver according to the present invention depicting the expandable bit in its unexpanded position; I

FIG. 2 is an end view of the screwdriver of FIG. 1;

FIG. 3 is a fragmentary perspective of the screwdriver of FIG. 1 depicting the expandable bit in its expanded position. i

FIG. 4 is an end view of the screwdriver of FIG. 3;

FIG. 5 is generally similar to FIG. 2 on somewhat-expanded scale and depicts the expandable bit inengagement with a screw having a straight screw slot;

FIG. 6 is similar to FIG. 5 and depicts a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS In FIGS. 1-5 of the drawings, wherein like parts bear like referenced numerals, there is shown a screw holding screwdriver including a handle 18 from which projects a longitudinally split two piece shank 20 terminating at its forward end in an essentially rectilinear expandable bit 21.

The shank 20 includes two resilient semicircular elongated superimposed parts 22 and 24 slidably encircled by a sleeve 26 which is longitudinally movable by a plastic annular projecting finger piece 28 secured to the rear of the sleeve. The shank members 22 and 24 slidably, overlappingly engage one another along their respective substantially flat inner cam or contact faces 32 extending longitudinally of the entire shank. The shank members further are progressively divergent from one another along these cam faces transversely to the length of the shank proceeding longitudinally forwardly thereof, as shown (FIG. 1), and as further illustrated and described in the aforementioned Osborn et al. and Barlow patents.

The expandable bit 21 according to the present invention comprises two overlapping driving tips 33a and 33b of reduced thickness on the front ends of the shank parts 22 and 24, respectively. The above described cam inclined to the inner cam faces 32; The bit faces 34 ex- 3 tend longitudinally along the outer surfaces of the shank members212;and;. 24 a distance corresponding to the depth of thescrew slotinto which the expandable bit is insertable until merging with outwardly inclined head surfaces 36 which inturn merge with the rearward ungrounded semicircular portions of the shank parts 22 and 24, as shown (FIGS, 1 and 3). The bit faces 34 are of th e bit faces 34 is desirable when the screwdriver is used with screws having dovetail slots. Such screws are easily mounted on the expandable bit of the present invention by vertically inserting the bit into the slot and thereafter expanding the bit without slipping or rocking the bit into the slot from the side thereof. A screw when thusly mounted on the expandablebit is held by the dovetail connection therebetween; but also is gripped and is prevented from'slipping sideways off the bit by engagement of the bit faces 34 with the sides of the screw slot. This results in a positive mounting which is reliable and easy to use with improved accuracy in the placement of .driven screws. It will be recognized, however,,that.the expandable bit according to the present invention also-can be used with standard straight screw slots and alternatively need not be formed with the latter taper of ,thebit faces 34.

As best shown in FIG. 5, the bit faces 34 are inclined at an anglela to the cam faces 32 and hence each driving tip has an inwardly diminishing tip thickness proceeding transversely to the length of the shank. Only the relatively thin inner portions of the driving tips 33a and 33b overlap each other at the unexpanded position of the bit (FIG. 2) with their relatively thick outer portions projecting transversely outwardly, as shown, due to the above described forward divergence of the shank parts 22 and 24. The, unexpanded composite central thickness T of the overlapping inner portions of the driving tips 33:: and 33b is slightly greater than the individual thicknesses'T- of their relatively thick outerportions. Thus, the bit faces 34 of each driving tip are coextensive with mutually parallel longitudinal planes which are offset laterally from the outer edges of the cam face 32 associated with the other driving tip, as depicted by transversely projecting broken lines 36 in FIG. 5. It will be apparent that the thickness of the expandable bit 21 can be varied depending upon the width of the screw a. in screw S by varying the angle a.

Operation of the expandable bit 21 of the present invention may now be understood by comparing FIGS. 1-4 of the drawings wherein the bit is depicted at its unexpanded or thinnest (FIGS. 1 and 2) and expanded or thickest (FIGS. 3 and 4) positions. By comparing FIGS.

2 and 4 it will be seen that by sliding the sleeve 26 forwardly along the shank 20, the forward divergent portions of the shank members 22 and 24 and hence the driving ,tips 331: and 3317 are progressively wedged or driven inwardly along their cam faces 32 into greater overlapping. relationship with one another. Simultain FIG. 1 the forward end of the ex-' neously,;the bit faces 34. are laterally separated from separation A, at their unexpanded position (FIG. 2) to separation A at their expanded position (FIG. 4).

Thus, itwill beseen that the driving tips of the expandable bit of the-present invention are in continual abutting unyielding engagement with one another .along the diagonal slip plane therebetween defined by their respectively associated cam faces 32. The diagonal slip plane extends transversely across a major portion of the expandable bit 21 between the bit faces 34 and provides a stronger, more rigid, unyielding bit without the disadvantages of an expandable bit of the type illustrated and described in the aforementioned Osborn et al. and Barlow patents.

A second preferred embodiment of the present invention, depicted in FIG. 6, comprisesa generally similar expandable bit to that already illustrated and described; but which tends to be self-centering longitudinally of a straight screw slot. This beneficial result occurs because the outer bit faces 34' are inclined at an angle b which is greater than the aforementionedangle a relative to the cam faces 32'. The unexpanded composite central thickness T of the overlapping relatively thin inner portions of the driving tips is less than the individual thicknesses T of their relatively thick outer portions. Hence, the middle overlapping portions of the driving tips 33a and 33b define opposite generally V- shaped outwardly opening notches on either screw slot engageable side of the bit.

As a self-centering expandable bit, the expandable bit of FIG. 6 is particularly useful with round headed screws having straight slot openings which are narrower than the outer individual thicknesses T of the driving tips and which have head slot lengths less than the unexpanded width of the bit. The bit is insertable vertically into such a screw slot with the thick outer wedge portions of each driving tip respectively projecting outwardly from either end of the screw slot and longitudinally thereof. The bit is centered longitudinally within the screw slot in response to engagement of the cam faces 32 with respective opposite ends of the screw slot as the bit is expanded in the manner already described. The expandable bit depicted in FIG. 6 is also useful with screws having screw slots within which the outer relatively thick portions of the driving tips 33a and 33b are insertable, although when so used it doe not tend to be self-centering.

The expandable bit depicted in FIG. 6 fits a wider range of screws fitted with straight slots or difi'erent widths than the bit of FIGS. 1-5 because of its relatively large thickness variations between the individual outer tip thicknesses T and the composite central thickness T,-,. For example, the bit of FIG. 6 with outer tip thicknesses T of 0.063 inches and unexpanded composite thickness T of 0.050 inches will fit a screw slot 0.054 inches wide and will also fit a slot 0.064

inches wide. It will be appreciated, however, that when used with the 0.064 inch screw slot the bit of FIG. 6 is not self-centering. However, the bit depicted in FIGS. I-5 if made to fit a screw having a slot width of 0.064 inches typically has an unexpanded composite thickness T of 0.062 inches and outer individual thicknesses T of 0. 060 inches. It will be apparent that the latter bit will not fit a screw slot 0.054 inches wide.

Thus, it will be appreciated that by this invention there is provided a highly effective screw holding screwdriver having an improved expandable bit by which the abovementioned objectives are completely fulfilled. It also will be appreciated that various modifications and/or changes can be made in the embodiments described without departure from the spirit or scope of the present invention. It is to be understood, therefore, that the foregoing description is illustrative of only two preferred embodiments, not limiting. and that the true spirit and scope of the present invention will be determined by reference to the appended claims.

What is claimed is:

1. An expandable bit screw-holding screwdriver comprising:

a. a handle;

b. an elongated split shank having one end affixed to said handle, said elongated split shank comprising two identical elongated sections, one lying on either side of the longitudinal axis defined by said elongated split shank, each of said sections includl a flat contact face extending substantially the entire length of said section and being substantially equal in width to the width of said section, said flat contact faces of said sections lying in overlapping contacting engagement with one another along substantially their entire length, the amount of said overlap decreasing with distance at least near the end of said elongated split shank remote from the end thereof affixed to said handle;

2. an overlapping driving tip formed in the end of said section remote from the end of said elongated split shank affixed to said handle, the overlapping driving tips of both of said sections cooperating to form an expandable screwdriver bit, each of said overlapping driving tips being wedge-shaped over their entire width when viewed in a plane orthogonal to the longitudinal axis of said elongated split shank, one surface of said wedge-shape being defined by the flat contact face of said section, the other surface of said wedge-shape defining a bit face, said bit face diverging inwardly with respect to said flat contact face when viewed in said plane orthogonal to said longitudinal axis of said elongated split shank, said bit face also tapering inwardly toward said handle and said longitudinal axis; and,

3. an outer-tip-divergence-control surface extending substantially the entire distance between said handle and said overlapping driving tip; and,

c. a sleeve slidably mounted on said elongated shank about said outer-tip-divergence-control surfaces of said sections, said sleeve including an aperture shaped similar to the shape of said outer-tipdivergence-control surfaces and equal in size to the size of said outer-tip-divergence-control surfaces when said sections fully overlap one another, whereby movement of said sleeve toward said overlapping driving tips of said sections increases the amount of section overlap in the region of said overlapping driving tips, the increase in overlap moving said bit faces away from one another, said sleeve being slidably movable between an unexpanded driving tip divergence position whereat the sleeve is near said handle and an expanded driving tip divergence position whereat the sleeve is near said overlapping driving tips of said sections.

2. An expandable bit screw-holding screwdriver as claimed in claim 1, wherein the unexpanded composite central thickness between said bit faces, when said sleeve is in said unexpanded driving tip divergence position, is less than the maximum thickness between the flat contact face and the bit face of said wedges.

* =l =l= l 

1. An expandable bit screw-holding screwdriver comprising: a. a handle; b. an elongated split shank having one end affixed to said handle, said elongated split shank comprising two identical elongated sections, one lying on either side of the longitudinal axis defined by said elongated split shank, each of said sections including:
 1. a flat contact face extending substantially the entire length of said section and being substantially equal in width to the width of said section, said flat contact faces of said sections lying in overlapping contacting engagement with one another along substantially their entire length, the amount of said overlap decreasing with distance at least near the end of said elongated split shank remote from the end thereof affixed to said handle;
 2. an overlapping driving tip formed in the end of said section remote from the end of said elongated split shank affixed to said handle, the overlapping driving tips of both of said sections cooperating to form an expandable screwdriver bit, each of said overlapping driving tips being wedge-shaped over their entire width when viewed in a plane orthogonal to the longitudinal axis of said elongated split shank, one surface of said wedge-shape being defined by the flat contact face of said section, the other surface of said wedge-shape defining a bit face, said bit face diverging inwardly with respect to said flat contact face when viewed in said plane orthogonal to said longitudinal axis of said elongated split shank, said bit face also tapering inwardly toward said handle and said longitudinal axis; and,
 3. an outer-tip-divergence-control surface extending substantially the entire distance between said handle and said overlapping driving tip; and, c. a sleeve slidably mounted on said elongated shank about said outer-tip-divergence-control surfaces of said sections, said sleeve including an aperture shaped similar to the shape of said outer-tip-divergence-control surfaces and equal in size to the size of said outer-tip-divergence-control surfaces when said sections fully overlap one another, whereby movement of said sleeve toward said overlapping driving tips of said sections increases the amount of section overlap in the region of said overlapping driving tips, the increase in overlap moving said bit faces away from one another, said sleeve being slidably movable between an unexpanded driving tip divergence position whereat the sleeve is near said handle and an expanded driving tip divergence position whereat the sleeve is near said overlapping driving tips of said sections.
 2. an overlapping driving tip formed in the end of said section remote from the end of said elongated split shank affixed to said handle, the overlapping driving tips of both of said sections cooperating to form an expandable screwdriver bit, each of said overlapping driving tips being wedge-shaped over their entire width when viewed in a plane orthogonal to the longitudinal axis of said elongated split shank, one surface of said wedge-shape being defined by the flat contact face of said section, the other surface of said wedge-shape defining a bit face, said bit face diverging inwardly with respect to said flat contact face when viewed in said plane orthogonal to said longitudinal axis of said elongated split shank, said bit face also tapering inwardly toward said handle and said longitudinal axis; and,
 2. An expandable bit screw-holding screwdriver as claimed in claim 1, wherein the unexpanded composite central thickness between said bit faces, when said sleeve is in said unexpanded driving tip divergence position, is less than the maximum thickness between the flat contact face and the bit face of said wedges.
 3. an outer-tip-divergence-control surface extending substantially the entire distance between said handle and said overlapping driving tip; and, c. a sleeve slidably mounted on said elongated shank about said outer-tip-divergence-control surfaces of said sections, said sleeve including an aperture shaped similar to the shape of said outer-tip-divergence-control surfaces and equal in size to the size of said outer-tip-divergence-control surfaces when said sections fully overlap one another, whereby movement of said sleeve toward said overlapping driving tips of said sections increases the amount of section overlap in the region of said overlapping driving tips, the increase in overlap moving said bit faces away from one another, said sleeve being slidably movable between an unexpanded driving tip divergence position whereat the sleeve is near said handle and an expanded driving tip divergence position whereat the sleeve is near said overlapping driving tips of said sections. 